1. Field of the Invention
This invention relates to improvements in high temperature secondary batteries and especially lithium aluminium iron sulphide (LAIS) batteries.
2. Discussion of Prior Art
High temperature secondary batteries have been known for some years. Compared to conventional lead/acid batteries high temperature secondary batteries can offer similar performance but at only 1/3 the weight and volume. They are formed as an electrolyte separator material sandwiched between an anode and cathode. In the case of a LAIS battery the cathode is ferrous sulphide, the electrolyte is lithium halide and the anode is lithium aluminium alloy. LAIS and related batteries utilise the high power density afforded by the lithium sulphur couple. However the use of these and other high temperature secondary batteries as high power/high energy batteries has been hampered by various factors such as maintaining conductivity efficiency over many charge/discharge cycles and problems associated with dimensional stability on heating and cooling as batteries are charged and discharged. In certain instances changes in dimensional stability are so severe as to result in internal breakdown of the battery rendering it useless. Where the effects are less severe internal expansion of the battery may cause damage by leakage of electrolyte.